Artificial electric line



April 14, 1925. 1,533,178

J. J. GILBERT ARTIFICIAL ELECTRIC LINE Filed lflay 19. 1922 3Sheets-Sheet 1 April 14, 1925. 1,533,178 J. J. GILBERT ARTIFICIALELECTRIC LINE Filed May 19. 1922 s Sheets-Shed 2 April 14, 1925.1,533,178

J. J. GILBERT v ARTIFICIAL ELECTRIC LINE Filed May 19. 1922 :5Sheets-Sheet 5 Patented Apr. 14, 1925.

UNITED, STATES PATENT OFFICE.

JOHN J. GILBERT, OF PORT WASHINGTON, NEW YORK, ASSIGNOR T WESTERN ELEC-TRIO COMPANY, INCORPORATED, OF NEW YORK, N, Y., A CORPORATION OF NEWYORK.

Application filed May 19,

To all whom it may concern:

Be it known that I, JOHN J. GILBERT, a citizen 'of the United States ofAmerica, re

siding at Port Washington, in the county 6 of Nassau and State of NewYork, have invented certain new and useful Improvements in ArtificialElectric Lines, of which the following is a full, clear, concise, andexact description.

This invention relates to submarine cable systems and to artificiallines particularly adapted for such systems but also capable of otheruses to which networks of this general form are adapted.

16 An objectof this invention is to provide a submarine cable duplexsystem adapted for o eration at higher speeds than those now 0 tainable.

Another object is to provide an artificial 20 line capable of moreexactly balancing the impedance of a cable or other transmission linethan those now in use.

Another object is to provide an improved form of electric network ofgeneral application.

The invention may be understood from the following description andaccompanying drawings. Fig. 1 is a diagrammatic showing of the terminalapparatus of a sub- 3 marine telegraph cable; Figs. 2, 2 and 2 arecurves used in explanation of the invention; and Figs. 3 to 8 inclusiveare diagrammatic showings of various modifications of the invention.

a5 Referring to Fig. 1 the submarine cable X terminates in the usualduplex bridge arrangement in which the transmitter T and the receivingcircuits R, C are conjugately related, the artificial line N providing ahal- 40 ance for the cable which prevents transmitted currents fromaffecting the local receiver. The essential property of the artificialline N'is that, in a given range of frequencies, it shall have the sameimpedance as the cable. It usually is of the form shown in Fig; 3without elements L, Z, 1'.

The amplitude of the received signal is dependent upon the signalingspeed, which must therefore be such that the received signal is legiblethrough the disturbance due to unbalance. If by any means the magnitudeof this disturbance can be reduced the speed of operation can beincreased until ARTIFICIAL ELECTRIC LINE.

1922. Serial N0. 582,064.

the amplitude of the received signal again reaches the limit set by.unbalance. A telegraph message consisting of a succession of positiveand negative pulses can be considered as composed of a number ofsinusoidal currents of all frequencies added together, the relativeamplitudes of the various components being determined by the characterand arrangement of the si a1 pulses. It is found that in order to estpreserve the legibility of the message it is necessary to preserve theamplitude relations of all components up to a certain frequency. Thisfrequency bears a certain definite relation to the frequency of theshortest pulses of the signals, the relation depending upon the code andmethod of reception used., In the caseof the standard cable code, withrecorder working, the signal frequency is roughly equal to the reversalfrequency or to one-half the dot frequency. When a signal is transmittedover a submarine cable the amplitudes of all the frequency componentsare reduced, the loss suffered at any frequency being greater the higherthe frequency. It is evident therefore, that many frequencies which arenotpresent in a received signal will be present in the transmittedsignal, and therefore the range of frequencies for which accuratebalance of a duplex systemris required extends beyond the signalfrequency: in fact, the limit 85 of this range may be two or three timesthe signal frequency. It is desirable, therefore, that in a, duplexsystem the differences between the transmission constants of the cableand of the artificial line be reduced as far as possible for all valuesof frequency in the above mentioned range, exact balance for frequenciesoutside this range not being absolutely essential. This means that theresistance and inductance of the artificial line should be made as faras possible equal to the resistance and inductance of the cable at allfrequencies inside this range.

The practice of using an artificial line such as that of Fig. 3 withelements L, Z and 100 r omitted, has been based upon the assumption thatthe effect of the cable inductance may be neglected and that the cableresistance is the same for all frequencies. It has been discovered,however, that due to the distribution of the return current in the seawater, the resistance of a submarine cable, even at low frequencies, isgreater than its value for steady currents and that the resistanceincreases with the frequency. It, has been found also that theinductance of,

the cable is not'negligible and is likewise dependent upon frequency.The' effect of ignoring these facts in designingan artificial line is alack of balance between the cable and the line at high frequencies withconsequent-disturbances in the receiving instrument- This inventionprovides a form of artificial line which takes all of these effectsintoaccount. I y

The impedance of an electric network de-' pends upon the characteristicimpedance K and the propagation constant P, which may be calculated bymeans of the formulae:

E i P (E+y'F) K 1 0 pg where and R, L and C arerespectivelytheresistance, inductance and capacity per unit length of line, p is 21:times the frequency and 1.: {1T v In the absence of irregularities theimpedance of a long submarine cable or an artithe range of frequencies.At very low frequencies, for instance, L is of minor importance comparedwith R and therefore at these frequencies comparatively large variationsofL can be permitted without affecting materially the variations in thetransmission constants. At higherfrequencies L becomes of increasingimportance and consequently the variations permitted are smaller. Inorder to compare the effect of variations of R and of L, curves may beplotted showing for a given difference between the impedance of-thecable and of the artificial line for each value of frequency Fthroughout the range employed the corresponding permissible differences(ZR and (ZL between the resistance and the inductance respectively ofthe cable and the line. Such curves are shown in Fig. 2*.

On account of the fact that the elements of the artificial line arelumped, additional terms should be included in formulae (1) which aretrue only for the case of uniformly distributed elements. The effect ofthese additional terms can always be made as capacity 0. In addition,one or more of the sections are provided with means for introduclnginductance and resistance whlch vary with impressed frequency In thesame manner as the cable. Each of these means comprises an inductance Lin inductive relation to a second coil Z which is in a closed circuitcontaining resistance 7'. If m denotes the mutual inductance of circuitsR, L and-r, l,

the effective resistance R and inductance L,

at the frequency f and Where 79:27: f are respectively z z In Fig.' 2 isshown a set of curves representing the relationship in a particular casebetween frequency of transmitted current insignal pulses per second'andeffective resistance and inductance, the former being in ohms perkilometer and the latter in mlllihenrys per kilometerQ Curves A and Bare for the effective resistance and inductance per kilometer of aparticularly long submarine cablev which isnot inductively loaded, andcurves C and- D give the effective values of the resistanceandinductance for the corresponding lengthof artificial line as com-.

puted from formulae (2) with properly chosen values of R, L, 1', Z andm. It can be seen that the condition previously stated is satisfied.namely, an equality of resistance of the cable and artificial line forlower frequencies, and equality of inductance for the higherfrequencies. The values ofthe constants employed in this calculationwere 11:1.443 ohms; r=.43 ohms; L=Z::2.432X 10- henrys; and m=1.82 10henrys.

For purposes of comparison calculations of the characteristic impedanceI were made for the above mentioned cable and for three differentdesigns of the corresponding artificial line. The results are shown inthe curves of Fig. 2", which represent the relation between thecharacteristic impedance I in ohms and the transmitted frequency insignal pulses per second. Curves 1 and 2 show the real and imaginaryparts respectively ofthe characteristic impedance of the cable. Thecorresponding quantities for the proposed type of artificial line areshown In order to obtain the flexibility necessaryfor balancing the lineand the cable it is desirable to construct part of the rimary resistanceR so that it can be varied. Condensers c and resistances 'r may likewisebe made variable, but it is ordinarily suflicient to provide a singlevariable element in each section. If inductance and resistance varyingwith frequency are to be associated wit but a single section of theartificial line, this should be the section nearest the transmitt-er T..It is preferred to associate such means with each of a plurality of thesections nearest the transmitter and to insertsimilar means at intervalsseparated by two or more sections throughout the remainder of theartificial line. A sufficient approximation to the. impedance of thecable can thus be obtained. I

In Fig. 4 is shown a type of artificial line which embodies the proposedprinciple and allows considerable economy' of space and material. Theresistance R, in this case serves as a secondary resistance for the.winding Z, and R functions similarly for Z The type of line shown inFig. 5 has the additional advantage that the characteristic impedance isexactly equal to that of the cable and is not subject to a correction onaccount of the lumping.

The advantages of the two preceding types of artificial line arecombined in the modification shown in Fig. 6.

'Fig. 7 shows a modified form of the invention in which a sleeve E ofconductive material surrounding the coil L takes the place of thesecondary inductance l and resistance 1' of Fig. 3. Item be seen fromequation (2) above that the quantities '1", Z.

may be varied at will providing, the ratios M /LZ and 1 /1 be keptconstant. This al lows a flexibility of design which permits the use ofthe modification shown in Fig. 7, when it is possible thereby to obtainthe proper values of these variables.

There is shown in Fig. 8 a modification of the form of the invention ofFig. 7 with the substitution of a laminated core of materialot highpermeability forthe sleeve E of Fig. 7.

The preceding discussion has been entirely with reference to non-loadedcables.

' The invention, however, may be equally well 4 v I e I applied to anartificial linehavlng the transmiss on characteristics of a cable ortransmission line. in which the inductance has been increased by meansof loading. The

additional factor of increased resistance due to losses in the loadingmaterial may be taken care of by the methods above described. in thiscase the loading may be so heavy that the total inductance issubstantially constant. the resistance alone varying with the frequency.Or 'the loading may be of a kind or degree which will necessitate"s'istive circuit inductively associate the taking into account ofinductance and resistance variations due to changes in currentdistribution in the sea water and resistance variations due to variablelosses in the loading material.

Although the inventionwas developed for use in a submarine cable system,it is obvious that various features of the invention are capable of wideapplication. These features are therefore separately claimed.

What is claimed is:

1. An electrical signaling network comprisinga plurality of similarsections, each said sectioncomprising a shunt reactive element and aresistive circuit inductively associated with the section, the effectiveresistance of said resistive circuits being in series relation in :saidnetwork.

2. An electrical si aling network comprising a plurality 0 similarsections, each said section comprising a shunt capacity element and aresistive circuit inductively associated with the section, the'efiective resistance of said resistive circuits being in seriesrelation in said network. I

3. An electrical signaling network comprising a plurality of similarsections, each said section comprising a shunt capacity element, aseries resistance element, and a resistive circuit inductivelyassociated with the section, the efiective resistance of said circuitsbeing in series relation in said network. i 1

4. The combination of a signaling line having a resistance which variesover the range of si aling frequencies involved, of a termina balancingline for said signaling line comprising a plurality of similar sections,each said section comprising a capacity element in shunt relation to theline and a. resistance element in series relation to the line and partonly of said sections havin a rewith each section and in series relationto the balancing line.

5. The combination of a signaling line having a resistance which variesover the range of frequencies involved in signaling,

of a terminal balancing line for said siga terminal balancing line forsaid signalingline comprising a plurality of similar-sections, each saidsection havin a capacity element in shunt relation to said balancingline and a resistive element inductively related to said balancing lineand in series relation therewith, the resistance of said balancing linemore closely simulating'that of said slgnaling line at lowertransmitting frequencies and the inductance at higher transmittingfrequencies.

' .7. The combination with an inductively loaded submarine cable, ofmeans for transmitting si nals'thereover at such high speeds that theeective resistancevaries materiall within the range of frequenciesinvolve and a balancing line for said cable comprising a plurality ofsimilar sections, each said section comprising a capacity element inshunt relation to said balancing line and a resistive circuitinductively related to said balancin line and in series relationthereto, the e ective resistance of said line simulating the resistanceof the cable more closely in the lower portion of said frequency rangethan in the higher.

"8. The combination with a submarine cable having resistance andinductance each of which varies Withimpressed frequency over a certainrange of frequencies, of termmal apparatus for. said cable fortransmitting and receiving signals involving frequency components withinsaid range, and a terminal network for balancing said cable havininductance and resistance which vary with impressed frequencies, theresistance more closely simulating that of the cable at lower impressedfrequencies and the inductance at higher impressed frequencies.

9. An electrical si 'naling network comprising a plurality of similarsections, each said section comprising a shunt reactive elementandresistive elements on opposite sides of said reactive element, theresistive elements on corresponding sides ofthe sev eral sections beingin serles relation, circuits JOHN J. GILBERT.

my name this 16th day of May A. 1)., 1922 v

